Most fermentation products are soluble in the fermentation medium. Examples of such products are enzymes, amino acids and organic acids. This allows separation of the fermentation product from the cell mass by typical liquid-solid separation technologies (for example, centrifuges, filters or settlers). Fermentation products that are insoluble in an aqueous fermentation broth are often purified by extraction into a solvent in which the product is more soluble than the aqueous fermentation broth, thus, separating the product from the cell mass. Examples are sterols and lipids.
Products exist that are insoluble in an aqueous fermentation broth and for which the use of a solvent for extraction purposes is impossible or impractical. In such a case, the solid product of interest must be separated from both the solid cell mass phase and the liquid phase fermentation broth. Methods for such separations are not common. One possibility is to take advantage of any difference in particle size to filter the solids from one another. Another is to take advantage of differences in density and settle the solids at different rates, leading to separation. This invention shows that by actually solubilizing the cell mass, resulting in a liquid phase and solid (product-containing) phase, typical liquid-solid separation techniques can then be used to separate the solid product from the cell mass.